A World Health Organisation (WHO) database report has named Onitsha, in Nigeria’s South East, as the world’s most polluted city, alongside Zabol, an eastern Iranian city.
Worldwide air pollution is measured by minute particles, or particulate matter (PM), in the air. These particles are between 2.5 and 10 microns in diameter, roughly 30 times smaller than the width of a human hair.
The coarser PM10s include dust stirred up by cars on roads and the wind, soot from open fires and partially burned carbon from the burning of fossil fuels like coal, oil and wood. The particles are small enough to be inhaled deep into the lungs. But the ultra-fine particles known as PM2.5s can only be seen with microscopes and are produced from all kinds of combustion. These are small enough to get from the lungs into the blood supply and are possibly more deadly because they affect the cardiovascular system.
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Onitsha, with the highest for PM10s is one of Nigeria’s biggest commercial hubs and home to the famous river Niger/Niger bridge. Cars and trucks on the main road to Lagos belch fumes from burning low-quality diesel, and the air often stinks of burning waste from rubbish dumps, the smoke from old ships on the river and discharges from the metal workshops.
The WHO report reflects that an air quality monitor there registered 594 micrograms per cubic metre of microscopic PM10 particles, and 66 of the more deadly PM2.5s. Onitsha’s figures are nearly twice as bad as notoriously polluted cities such as Kabul, Beijing and Tehran and 30 times worse than London.
As a tropical port city which has doubled in size to over 1 million people in just a few years, it is frequently shrouded in plumes of black diesel smoke from old ships; it has no proper waste incineration plants; its construction sites and workshops emit clouds of dust and its heavy traffic is some of the worst in Nigeria.
A recent study of Onitsha’s water pollution found more than 100 petrol stations in the city, often selling low-quality fuel, dozens of unregulated rubbish dumps, major fuel spills and high levels of arsenic, mercury, lead, copper and iron in its water. The city’s many metal industries, private hospitals and workshops were all said to be heavy polluters emitting chemical, hospital and household waste and sewage.
Zabol, an eastern Iranian city has the highest for PM2.5s. It is on the border with Afghanistan, and was once at the heart of a bustling ancient civilisation, close to where the very first piece of animation came from in the form of an intricate pottery bowl dating back 5,000 years that displays a goat in motion. But the city is now a largely neglected area plagued by poverty – and polluted air, land and water.
Many cities in developing countries traditionally monitor only PM10s. But increasingly PM2.5 pollution is seen as the best measure of how bad air pollution is for health. Richer countries usually have higher levels of PM 2.5s, while low income countries have higher levels of PM10s. Both, says the WHO, are deadly.